Took me about 4 days to beat it on Veteran.
HOWEVER, I thought I'd be clever and start on Veteran to get all the campaign achievements in one go. NOT HAPPENING!!! Then went back, beat the game on Easy to get the layout, and then started again.
Some checkpoints are soooooo hard, but you get them eventually. The ones that are hardest are when your stupid squad do absolutely nothing and let you kill everyone. Ah well, it's done now.